It is often necessary in clinical medicine to interface blood with synthetic materials, such as in extracorporeal circuits, vascular replacements, artificial heart valves, catheters and other sensors and probes, and blood bags for storage purposes. Though a great deal of research effort has gone into the development of "blood-compatible" materials, most such materials and devices are still considered blood- incompatible or intolerable by clinicians. The vascular endothelium and blood cells consist of a gelatinous, carbohydrate-rich outer coat of high water content interfacing with plasma, producing an interface of very low interfacial tension. It is reasonable to model and study such interfaces as they are generally considered to be blood tolerable. Synthetic aqueous polymer networks (hydrogels) can be prepared with low interfacial tensions, high water contents, and apparent blood tolerability. It is proposed to model and study natural cell/plasma interfaces and synthetic gel/plasma interfaces to begin to understand the nature of interfacial blood tolerability and to develop interfaces suitable for eventual clinical cardiovascular applications. It is proposed to study the interfacial properties and plasma and blood compatibility of gel- grafted interfaces. It is further proposed to study the interfacial and blood properties as a function of water content and copolymer composition. The goal is to optimize the blood compatibility by control of water content, copolymer composition, and interfacial properties. Such gel interfaces may also serve as model systems for the study of cell surface phenomena.